"Each participant will receive 0.0005 BTC for making , at its choice, 1 unique tweet about Authorship."

We pay for just 1 tweet, not for several "unique" tweets.

"Each participant is allowed to claim 2 twitter accounts at most."

Some users own several Twitter accounts. We allow a participant to claim 2 accounts. Meaning, that only in this situation you could earn 2 x 0.0005 BTC.

For any other clarifications, please let me know.

-Peter